Field of the Invention
The present invention relates to a fluorescent probe, a singlet oxygen detection agent, or a singlet oxygen detection method.
Description of Related Art
Singlet oxygen (1O2) is an active species that attacks various molecules having unsaturated bonds or electron-rich molecules, and is used in various applied technologies, such as precise chemical synthesis, polymer science, photodynamic therapy (which hereinafter may also be referred to as “PDT”), wastewater or sludge treatments, and the like. Therefore, singlet oxygen is attracting attention.
PDT, as one of these technologies, is a method for treating diseased tissues of humans or other animals. The method is used to treat cancers and other diseases, and is performed by administrating a photodynamic therapeutic agent containing a photosensitizing substance, which generates reactive oxygen species, such as singlet oxygen, in response to light irradiation, to a patient through, for example, intravenous injection, and then locally irradiating the diseased tissue with light, thereby destroying only the diseased tissue by the generated reactive oxygen species.
The events that first occur after light irradiation during PDT are the generation and diffusion of singlet oxygen, as well as its reaction with peripheral molecules; these processes are considered to be closely related to the cytotoxicity of PDT (for example, see Non-patent Document 1, etc.). In actual medical practice, real-time observation of the generation and changes of singlet oxygen is very important to accomplish the fusion of diagnostic imaging and treatment (theragnostics), because the total amount of singlet oxygen generated by PDT directly influences the treatment progress, treatment efficiency, or the like.
Therefore, several singlet oxygen detection methods, typically a method for measuring the phosphorescence of singlet oxygen itself or a method using a fluorescent probe that produces luminescence by reacting with singlet oxygen, have been performed (for example, see Non-patent Documents 2, 3, etc.).
However, the method for measuring the phosphorescence of singlet oxygen itself requires the detection of low-energy phosphorescence, and therefore requires a special detector. This makes the method unrealistic; further, the spatial resolution is merely a single cell level (for example, see Non-patent Document 2, etc.).
In contrast, fluorescent probes for singlet oxygen detection enable the detection more easily than that in the measurement of phosphorescence of singlet oxygen itself, and therefore have been widely used.